Mirror signal iq-imbalance correction

ABSTRACT

A system and method are provided for calibrating the IQ-imbalance in a low-IF receiver. A Test Signal can be generated in a mirror frequency and conveyed to the receiver. The power of the signal produced in the receiver from the conveyed Test Signal can be measured. In the absence of an IQ-imbalance, the Test Signal can be completely eliminated in the receiver and the corresponding measured power of the produced signal can be minimized. Accordingly, a two dimensional algorithm is described for calibrating a receiver and correcting the IQ-imbalance by adjusting the phase and gain difference between the I and Q channels in the receiver based on the measured power of the signal produced in the receiver.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of allowed U.S. application Ser. No.13/960,584 entitled “MIRROR SIGNAL IQ-IMBALANCE CORRECTION,” filed Aug.6, 2013, which is a continuation of U.S. application Ser. No. 13/093,145entitled “MIRROR SIGNAL IQ-IMBALANCE CORRECTION,” filed Apr. 25, 2011,of which the full disclosure of these applications is incorporatedherein by reference for all purposes.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

FIELD OF THE INVENTION

This invention relates generally to the field of telecommunications, andmore specifically to correcting the IQ-imbalance in receivers thatgenerate in-phase (I) and quadrature-phase (Q) signals from an incomingcarrier signal in such systems.

BACKGROUND

In recent decades, among the most rapid technological advances havetaken place in the field of telecommunications. As consumers continue tocarry out more and more of their daily life's functions on mobiledevices, manufacturers are increasingly challenged to produce moreefficient, reliable, and faster systems capable of higher throughput. Inaddition, the devices are expected to perform in sub-optimal conditionssuch as in varying temperatures, in moving vehicles, and with highlydistorted and attenuated signals, while conserving power and being ascost-efficient to build as possible.

Generally, mobile telecommunications devices receive a carrier-frequencysignal that is processed in the receiver before information can beextracted from the signal. To achieve high performance and stability,the receiver has to function with accuracy and consistency under variousconditions, such as changing temperatures, and across differentchannels. However, because the performance of receivers can be highlysensitive to such factors, the problem of achieving consistently highperformance can be challenging. What is needed is a system and methodfor accurately and efficiently calibrating a receiver for optimalperformance in various conditions. As will be demonstrated, thisinvention meets this need in an elegant manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a RF receiver in accordance with variousembodiments.

FIG. 2 illustrates an example of a mirror frequency signal, inaccordance with various embodiments.

FIG. 3 illustrates an example of a single tone mirror frequency TestSignal, in accordance with various embodiments.

FIG. 4 is a flow diagram of an example calibration process in a low-IFreceiver in accordance with various embodiments.

FIG. 5 illustrates an example of a low-IF receiver with a calibrationmechanism, in accordance with various embodiments.

FIG. 6 illustrates a further example of a low-IF receiver with acalibration system, in accordance with various embodiments.

FIG. 7 illustrates an example of an IQ Imbalance Compensator, inaccordance with various embodiments of the invention.

FIG. 8 illustrates a two-dimensional space representing Gain Imbalanceand Phase Imbalance in a search algorithm, in accordance with variousembodiments.

FIG. 9 illustrates a 2^(nd) Stage Searching Area representing GainImbalance and Phase Imbalance in a search algorithm, in accordance withvarious embodiments.

FIG. 10 illustrates an example process flow of a searching algorithm,such as the algorithm described in FIG. 8 and FIG. 9, in accordance withvarious embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention.However, it will be apparent to one skilled in the art that the presentinvention can be practiced without these specific details. In otherinstances, well known circuits, components, algorithms, and processeshave not been shown in detail or have been illustrated in schematic orblock diagram form in order not to obscure the present invention inunnecessary detail. Additionally, for the most part, details concerningcommunications systems, transmitters, receivers, communications devicesand the like, have been omitted inasmuch as such details are notconsidered necessary to obtain a complete understanding of the presentinvention and are considered to be within the understanding of personsof ordinary skill in the relevant art. It is further noted that, wherefeasible, all functions described herein may be performed in eitherhardware, software, firmware, analog components or a combinationthereof, unless indicated otherwise. Certain terms are used throughoutthe following description and Claims to refer to particular systemcomponents. As one skilled in the art will appreciate, components may bereferred to by different names. This document does not intend todistinguish between components that differ in name, but not function. Inthe following discussion and in the Claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”

Embodiments of the present invention are described herein. Those ofordinary skill in the art will realize that the following detaileddescription of the present invention is illustrative only and is notintended to be in any way limiting. Other embodiments of the presentinvention will readily suggest themselves to such skilled persons havingthe benefit of this disclosure. Reference will be made in detail toimplementations of the present invention as illustrated in theaccompanying drawings. The same reference indicators will be usedthroughout the drawings and the following detailed description to referto the same or like parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith applications and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

In various embodiments, systems and methods are described for correctingan in-phase (I) and quadrature-phase (Q) imbalance, otherwise known asan “IQ imbalance,” in a low intermediate frequency (low-IF) receiver.FIG. 1 illustrates an example of a structure of a typical low-IFreceiver. A radio frequency (RF) signal, or a carrier signal, can bereceived at an antenna 100 and conveyed to the receiver input (RF Input)101. The signal can be conveyed to a low noise amplifier (LNA) 102 andto a radio frequency filter (RF Filter) 104. After the RF Filter 104,the signal can be separated into two channels, an in-phase (I) Channeland a quadrature-phase (Q) Channel. On the I Channel, the signal can beconveyed to a mixer 106, where the signal can be mixed with azero-degree phase signal from a local oscillator (LO 0°) 107 and theproduced signal can be conveyed to an amplifier 110. On the Q Channel,the signal can be conveyed to a mixer 108, where the signal can be mixedwith a ninety-degree phase signal from a local oscillator (LO 90°) 109and the produced signal can be conveyed to an amplifier 112. The IChannel and the Q Channel can then be conveyed to a Poly Phase Filter114, to an Intermediate Frequency Variable Gain Amplifier (IF VGA) 118,which can have a level of amplification that is controlled by a controlsignal (Gain Control) 116, to a filter 120, to an amplifier 122, and tothe receiver output (Output) 124.

In the ideal case, both the signal produced on the I Channel and thesignal produced on the Q Channel will have the same voltage gain and a90 degree difference in phase. If the produced I signal and the producedQ signal have different gain, then a gain imbalance is present, if thephase difference between the produced I signal and the produced Q signalis smaller or larger than 90 degrees, then a phase imbalance is present.Presence of either a gain imbalance or a phase imbalance is referred toas an IQ imbalance. Various factors can contribute to an IQ imbalance ina receiver, including a phase mismatch between LO signals 107, 109, gainand delay or phase mismatch in mixers 106, 108, gain mismatch inamplifiers 110, 112, and mismatches in the components of a Poly PhaseFilter 114.

Implementing low-IF topology in radio frequency (RF) receivers hasseveral advantages. For example, low-IF topology supports DC-frequencyand can reduce the size and power consumption of an RF receiver.However, a drawback of low-IF receivers is a tendency towards mismatchin gain and phase between the I and Q channels; in other words, the IQimbalance. In most low-IF receivers, a multi-channel topology and atleast one Saw-filter are used to reduce the IQ-imbalance problem.However, such topologies can be large in size, expensive to produce, andcan consume a lot of power. In various embodiments, systems and methodsare described to correct the IQ-imbalance effect on the SNR performancein low-IF receivers by estimating the IQ-imbalance and compensating itby adjusting the gain and phase mismatch between the “I” and “Q” path.

Further, when a signal in a mirror frequency is conveyed to a low-IFreceiver, an IQ imbalance can decrease the signal to noise ratio (SNR)performance of the receiver. FIG. 2 illustrates an example of a mirrorfrequency signal, in accordance with various embodiments. As illustratedin the example of the figure, mirror frequency signals 202 can be areflection of the desired channel 200 over the local oscillatorfrequency (LO Frequency) 204. For example, if a desired channel is 500MHz to 600 MHz and the LO Frequency is at 400 MHz, mirror frequencysignals will be 100 MHz (400 MHz−(600 MHz−400M Hz)) to 300 MHz (400MHz−(500 MHz−400 MHz)) signals. In the presence of a signal in a mirrorfrequency, an IQ imbalance can cause undesired mirror signal folding tothe desired channel, decreasing the in-band signal to noise ratio (SNR)and creating an adjacent channel performance shortage. When there is notan IQ imbalance, all signals in mirror frequencies can be filtered out.

In various embodiments, mirror frequency signals can be used tocalibrate a low-IF receiver to compensate for an IQ imbalance. Namely, aTest Signal, which Test Signal can be a mirror frequency signal for adesired channel, can be generated in an oscillator and conveyed to thereceiver. The power of the signal produced in the receiver can bemeasured to determine if the Test Signal has been filtered out. If theTest Signal has not been filtered out, then the phase and/or gain of theI and/or Q channel in the receiver can be changed to adjust the IQimbalance. The power of the signal produced in the receiver from theTest Signal can then be measured again and the process can continueuntil the power of the signal produced in the receiver from the TestSignal is minimized and the IQ imbalance has, accordingly, beencorrected. The generated Test Signal can be a single tone signal in amirror frequency. In various embodiments, calibration of a receiver canbe performed for any desired channel. Namely, different channels canhave different optimal calibration settings in a receiver, hence,calibration can be performed for each channel. For example, the devicecan be calibrated when a new channel is selected in the receiver. Invarious embodiments, the device can be calibrated periodically. In otherembodiments, the device can be calibrated whenever poor performance isdetected.

In this specification, “gain imbalance” refers to the difference in gainbetween the I and the Q channels. In the absence of a gain imbalance,the I and the Q channel are of equal gain. Accordingly, “adjusting” again imbalance refers to changing the gain by either increasing ordecreasing the gain of the I and/or the Q channel such that the gaindifference between the channels is changed.

In this specification, “phase imbalance” refers to the difference inphase between the I and the Q channels. In the absence of a phaseimbalance, the I and the Q channel are perfectly 90 degrees out ofphase. Accordingly, “adjusting” a gain imbalance refers to changing thephase by either increasing or decreasing the phase of the I and/or the Qchannel such that the phase difference between the channels is changed.

FIG. 3 illustrates an example of a single tone mirror frequency TestSignal, in accordance with various embodiments. As illustrated in theexample of FIG. 3, a Test Signal 302 can be a single tone signal withinthe range of mirror frequencies 301 of the desired channel 300 asreflected over the local oscillator frequency (LO Frequency) 304. Forexample, if a desired channel is 500 MHz to 600 MHz and the LO Frequencyis at 400 MHz, a Test Signal can be any signal in the 100 MHz (400MHz−(600 MHz−400 MHz)) to 300 MHz (400 MHz−(500 MHz−400 MHz)) range.Ideally, however, the Test Signal will closer to the middle of themirror frequency range.

FIG. 4 is a flow diagram of an example calibration process in a low-IFreceiver in accordance with various embodiments. A desired channel canbe selected 402 in the receiver. The gain imbalance and/or phaseimbalance can be adjusted 406. The adjusting of the gain imbalanceand/or phase imbalance 406 can be performed, for example, according topredetermined procedures and decisions contained in the device'scircuits or digital logic. For example, the gain of the I or the Qchannel can be increased or decreased or the phase shift of the I or theQ channel can be increased or decreased. A Test Signal in a mirrorfrequency can be generated for the desired channel and conveyed to thereceiver 404. The power of the signal produced in the receiver for thenew gain and/or phase settings can then be measured 408. A decision canbe made as to whether the last stage of the calibration process has beenreached 410; for example, whether the last stage has been reached can beindicated by predetermined algorithms, procedures, and executable logiccontained in the device's circuits or digital logic. If the last stagehas not been reached, then the gain imbalance and/or phase imbalance canbe adjusted 406 and the process can repeat. If the last stage has beenreached, then the gain and phase settings corresponding to the lowestmeasured signal power and accordingly corresponding to the lowest IQimbalance can be used to calibrate the receiver 412. Namely, the gainand phase adjustment values corresponding to the settings with thelowest observed IQ imbalance or the lowest measured power of theproduced signal can be used in operating the receiver under the desiredchannel. The adjusting of the gain imbalance and/or phase imbalance 406can be performed according to various algorithms, procedures, orexecutable logic. For example, in one embodiment, the phase and gain canbe adjusted 406 in predetermined increments, such as by increasing thegain by a certain number of decibels at a time on the I channel andincreasing the phase by a certain number of degrees at a time on the Ichannel. The power of the signal produced in the receiver can bemeasured 408 between each adjustment and a decision 410 that the laststage of the procedure has been reached can be made when, for example,all of a predetermined set of adjustment have been performed and thecorresponding signal power has been measured, or when the measuredsignal power is below a predetermined threshold, indicating that the IQimbalance has been sufficiently corrected. In various embodiments,feedback loops can be implemented to change the gain and phase whileobserving the power of the signal produced in the receiver to determineideals gain and phase settings. Further methods for adjusting the gainand phase 406 and deciding 410 to use certain values of gain and phasewill be discussed further below.

FIG. 5 illustrates an example of a low-IF receiver with a calibrationmechanism, in accordance with various embodiments. A Test Signal (RFTest Signal) 500 can be conveyed to a receiver (Low IF Receiver) 502.Such a Test Signal 500 can be generated in an oscillator. The signal canbe a single tone signal in a mirror frequency for the desired channel towhich the receiver is tuned. A phase and gain compensator 504 can adjusta gain imbalance and a phase imbalance in the receiver 502 by adjustingthe gain difference and/or the phase difference between the I and the Qchannels. An intermediate frequency signal (IF) 508 produced in thereceiver 502 can be conveyed to an analog to digital converted (ADC) 506for conversion to the digital domain. The digital signal 528 can beconveyed to a power estimator 510, where the signal's 528 power can bemeasured, and the power estimate (Power Estimate) 512 can be conveyed toan IQ Imbalance Estimator 514, where, based on the measured signal power512 and according to executable logic in the IQ Imbalance Estimator 514,a gain imbalance estimate (Gain Imbalance Estimate) 516 and a phaseimbalance estimate (Phase Imbalance Estimate) 518 can be generated andconveyed to an analog circuit interface (Analog Circuit Interface) 522,where the gain imbalance estimate 516 and the phase imbalance estimate518 can be converted to the analog domain. The analog phase error (PhaseError) 524 and the analog gain error (Gain Error) 526 can be conveyed tothe Phase and Gain Compensator 504. The Phase and Gain Compensator 504can adjust the phase imbalance and gain imbalance in the receiveraccording to the receiver Phase Error 524 and Gain Error 526. Abase-band gain control signal (Base-Band Gain Control) 520 can begenerated in the IQ Imbalance Estimator 514 according to executablelogic in the IQ Imbalance Estimator 514 and conveyed the receiver. Thebase-band gain control signal 520 can adjust the gain in the base-bandsection by, for example, adjusting a gain in a variable gain amplifierin the base-band section of the receiver 502. In an embodiment, thebase-band gain can be increased as the power of the signal produced inthe receiver 508 decreases to increase the power estimate 512 andthereby allow more precise calibration of the system.

Thus, in the example of FIG. 5, if the receiver 502 does not exhibit anIQ imbalance, then all mirror frequencies and, accordingly, the entireTest Signal 500 will be eliminated and the Power Estimate 512 will beminimal. Conversely, in the presence of an IQ imbalance, some of theTest Signal can appear after the receiver 502. Hence, by minimizing thePower Estimate 512 through adjusting the gain imbalance and the phaseimbalance, the system can be calibrated to correct the IQ imbalance.Accordingly, various algorithms can be implemented in the system and inthe IQ Imbalance Estimator 514 to calibrate the system.

In an embodiment, a Power Estimate 512 can be measured for a first setof phase imbalance and gain imbalance value combinations. A first idealcombination producing the lowest Power Estimate 512 can be selected outof the first set of combinations and a second, more precise, set ofphase imbalance and gain imbalance value combinations can be selectedbased on the first ideal combination. A Power Estimate 512 can bemeasured for the second set of phase imbalance and gain imbalance valuecombinations and a second ideal combination can be similarly selected.The process can continue with a more accurate ideal combination of gainand phase imbalance values being derived in each iteration. Because gainimbalance and phase imbalance can be inter-related, such a process wherecombinations of phase imbalance and gain imbalance are tested orsimultaneously varied can provide more accurate or faster calibration.

In various embodiments, the gain imbalance and the phase imbalance canbe adjusted in a feedback loop based on the Power Estimate 512. Forexample, the gain imbalance can be adjusted in steps of predeterminedincrements and the Power Estimate 512 can be measured between each step,the gain adjustment at minimal Power Estimate 512 can correspond to theleast gain imbalance. For example, the gain on the I Channel can bechanged in steps of a certain number of decibels and the Power Estimate512 can be measured between each step. If the Power Estimate 512increases then the gain can be changed in the opposite direction. Theadjustment can continue in the direction of decreasing Power Estimate512 until the Power Estimate 512 starts to increase, the gain adjustmentcorresponding to the lowest Power Estimate 512 can correspond to thepoint of least gain imbalance. A similar feedback control system can beimplemented to adjust the phase imbalance. Further, because the phaseimbalance and the gain imbalance can be interrelated, the system can beconfigured to switch between calibrating the gain and the phase whileusing the best estimated gain or phase adjustment value for thenon-varied variable. For example, after finding a first initial optimalgain adjustment value, that value can be used while finding an initialoptimal phase adjustment value. After finding the initial optimal phaseadjustment value, a second optimal gain adjustment value can beestimated while using the first initial optimal phase adjustment valuein the receiver. In an embodiment, a feedback loop can be incorporatedwhere both the phase imbalance and the gain imbalance are simultaneouslyadjusted while the Power Estimate 512 is monitored to determine theideal gain and phase adjustments. In another embodiment, the calibrationcan be performed by selecting a range of gain or phase adjustments andmeasuring the Power Estimate 512 at predetermined increments on therange. For example, the gain adjustment corresponding to the lowestPower Estimate 512 can correspond to the adjustment with the lowestrespective gain imbalance. Similarly, the phase adjustment correspondingto the lowest Power Estimate 512 can correspond to the adjustment withthe lowest respective phase imbalance. After finding an initial gainadjustment value, the gain can again be tested for finer tuning on asmaller range of values, which range of values can be selected aroundthe initial gain adjustment value and where the gain will be testedbetween increments of adjustment. Similarly, finer tuning of the phaseadjustment can be performed. In another embodiment, as will be describedin further detail below, the gain and phase can be tested on atwo-dimensional space, wherein the gain adjustment values are on oneaxis and phase adjustment values are on the other axis, where the PowerEstimate 512 can be measured for a series of points in thetwo-dimensional space to find an optimal gain and phase imbalanceadjustment value.

FIG. 6 illustrates a further example of a low-IF receiver with acalibration system, in accordance with various embodiments. An RF signalcan be received at an antenna 600 and conveyed to an RF Input 602. Thesignal can be conveyed to a low noise amplifier (LNA) 604 to beamplified and the amplified signal can be conveyed to a radio frequencyfilter (RF Filter) 606 for filtering. After the RF Filter 606, thesignal can be conveyed down two channels, an I Channel and a Q Channel.On the I Channel, the signal can be conveyed to a mixer 608, where thesignal can be mixed with a 0 degree phase signal from a local oscillator(LO 0°) signal. On the Q Channel, the signal can be conveyed to a mixer610, where the signal can be mixed with a 90 degree phase signal from alocal oscillator (LO 90°) signal. After the mixers 608, 610, the signalscan be conveyed to an IQ Imbalance Compensator 612, where the phaseimbalance and gain imbalance can be compensated by adjusting the gaindifference and the phase difference between the I Channel and the QChannel. The signal on the I Channel can be conveyed to an amplifier 614and to a Poly Phase Filter 618. The signal on the Q Channel can beconveyed to an amplifier 616 and to the Poly Phase Filter 618 where theI Channel and the Q Channel can be combined into one intermediatefrequency signal. The signal can be conveyed to a variable gainamplifier 620 and to an intermediate frequency filter (IF Filter) 622.The signal can be amplified in an amplifier 624 and conveyed to thereceiver output 626. To calibrate the IQ imbalance on the systemdescribed in FIG. 6, the RF Input path can be turned off to prevent anyoutside signals from entering the system and a Test Signal 628 can beconveyed to the mixers 608, 610. In various embodiments, the calibrationcan be performed when a channel is switched. In various embodiments,calibration can be performed when performance is poor. The Test Signalcan be generated by an Auxiliary Synthesizer 629. In an embodiment, theAuxiliary Synthesizer 629 is a low cost ring oscillator synthesizer. Invarious embodiments, the Auxiliary Synthesizer 629 can be a synthesizerin addition to the high performance synthesizer generally present inreceiver chips to generate signals used in the mixer. In otherembodiments, the Auxiliary Synthesizer 629 can be a synthesizer alreadyavailable on the chip to perform other functions. In variousembodiments, an Auxiliary Synthesizer 629 without tight specifications,such as a synthesizer with high phase noise, frequency offset, and driftcan be implemented because the design can tolerate such conditions. TheTest Signal 628 can be a mirror frequency signal, such as a single tonesignal located in the mirror frequencies for the desired channel, asdescribed above. The Test Signal 628 can be separated into two channels,an I Channel and a Q Channel. On the I Channel, the signal can beconveyed to the mixer 608, where the signal can be mixed with a 0 degreephase signal from a local oscillator (LO 0°) signal. On the Q Channel,the signal can be conveyed to the mixer 610, where the signal can bemixed with a 90 degree phase signal from a local oscillator (LO 90°)signal. After the mixers 608, 610, the signals can be conveyed to the IQImbalance Compensator 612, where the phase imbalance and gain imbalancecan be compensated by adjusting the gain difference and the phasedifference between the I Channel and the Q Channel. The signal on the IChannel can be conveyed to the amplifier 614 and to the Poly PhaseFilter 618. The signal on the Q Channel can be conveyed to the amplifier616 and to the Poly Phase Filter 618. The I Channel and the Q Channelcan be combined into one intermediate frequency signal in the Poly PhaseFilter 618. The signal can be conveyed to the variable gain amplifier620 and to the intermediate frequency filter (IF Filter) 622. The signalcan be amplified in the amplifier 624 and conveyed to an analog todigital converter (ADC) 630 where it can be converted to the digitaldomain. In various embodiments, the ADC 630 could be Pipeline, flash, orany other type of ADC. The specification on the ADC can be broad. Invarious embodiments, the ADC resolution could be low, such as less than8 bits; because of the digital filtering and the feedback loops, the ADCis easier to design than a typical ADC with 8-12 bits. While a fasterADC with higher number of bits can perform better, in variousembodiments, a simple ADC could work because there is little pressure onthe ADC specifications. The digital signal can be conveyed to a DigitalPower Estimator 632, where a Power Estimate 636 of the signal can bemeasured and conveyed to an IQ Imbalance Estimator 634. In the IQImbalance Estimator 634, a digital gain imbalance estimate signal (GainImbalance Estimate) 638 and a digital phase imbalance estimate signal(Phase Imbalance Estimate) 640 can be produced based on Power Estimates636 according to algorithms in digital circuits. A Base-Band GainControl Signal 640 can be produced in the IQ Imbalance Estimatoraccording to algorithms in digital circuits to adjust the power in thevariable gain amplifier 620. The Gain Imbalance Estimate 638 and thePhase Imbalance Estimate 640 can be conveyed to the IQ ImbalanceCompensator 612. In the IQ Imbalance Estimator 634, an analog circuitcan compensate the phase imbalance and gain imbalance in the receiverbased on the Gain Imbalance Estimate 638 and Phase Imbalance Estimate640. This analog circuit will be described in more detail below.

In various embodiments, if the example of the system illustrated in FIG.6 does not exhibit an IQ imbalance, all of the Test Signal 628 can begone after the Poly Phase Filter 618. In the presence of a gain and/or aphase imbalance, some of the Test Signal 628 can remain after the PolyPhase Filter 618. Accordingly, when the Power Estimate 636 is at aminimum, the IQ imbalance in the system can also be at a minimum. Thus,various algorithms can be implemented in the digital circuits of the IQImbalance Estimator 634 to calibrate the system based on the PowerEstimate 636. Namely, in various embodiments, such algorithms can adjustthe gain imbalance and/or phase imbalance in the IQ ImbalanceCompensator 612 while monitoring the Power Estimate 636 to find the gainimbalance and phase imbalance adjustments that produce the lowest PowerEstimate 636 and the lowest corresponding IQ Imbalance. Further, suchalgorithms can vary the gain in the variable gain amplifier 620 to allowfor finer tuning of the gain imbalance and phase imbalance when thePower Estimate 636 reaches low levels. Such algorithms were discussed inthe context of FIG. 5 and further algorithms will be described in moredetail below.

FIG. 7 illustrates an example of an IQ Imbalance Compensator, inaccordance with various embodiments of the invention. Such an IQimbalance Compensator can adjust the gain imbalance and the phaseimbalance in a receiver based on a phase imbalance estimate (β) and again imbalance estimate (a) supplied from an IQ Imbalance Estimator,such as the Phase Imbalance Estimate 640 and the Gain Imbalance Estimate638 from the IQ Imbalance Estimator 634 of FIG. 6 or the Phase Error 524and Gain Error 526 from the IQ Imbalance Estimator 514 of FIG. 5. Suchan IQ Imbalance Compensator can be implemented in the example system ofFIG. 5 as the Phase and Gain Compensator 504 or in the example system ofFIG. 6 as the IQ Imbalance Compensator 612. In various embodiments, an IChannel signal (I) 702 and a Q Channel signal 704 can be conveyed to theIQ Imbalance Estimator. The I Channel signal 702 can be separated intotwo paths. On one path, the I Channel signal can be conveyed to an adder712; on a second path 714, the I Channel signal 702 can be multiplied bya Gain Imbalance Estimate (a) and conveyed to the adder 712. In theadder 712, the I Channel signal 702 can be added to the product of the IChannel signal 702 and the Gain Imbalance Estimate (a) to produce anadjusted I Channel signal (I₂) 706 such that I₂=I+αI. On the Q path, theQ Channel signal (Q) 704 can be conveyed to an adder 710. On anotherpath 716, the I Channel signal (I) 702 can be multiplied by a PhaseImbalance Estimate (β) and conveyed to the adder 710. In the adder 710,the Q Channel signal 702 can be added to the product of the I Channelsignal 702 and the Phase Imbalance Estimate (β) to produce an adjusted QChannel signal (Q₂) 708 such that Q₂=Q+βI. In various embodiments, α andβ could be either analog or digital signals. In a preferred embodiment,α and β are real numbers but in other embodiments α and β could becomplex signals. In an embodiment, the circuit is able to applyfrequency-dependent phase imbalance estimates and gain imbalanceestimates.

In various embodiments, a two-dimensional search algorithm can beimplemented in an IQ Imbalance Estimator to find optimum values of aGain Imbalance Estimate and a Phase Imbalance Estimate. Such atwo-dimensional algorithm can be implemented in digital circuits of anIQ Imbalance Estimator. For example, a two-dimensional search algorithmcan be implemented in an IQ Imbalance Estimator 634 to find a GainImbalance Estimate 638 and a Phase Imbalance Estimate 640 as describedin FIG. 6 or in an IQ Imbalance Estimator 514 to find a Gain ImbalanceEstimate 516 and a Phase Imbalance Estimate 518 as described in FIG. 5.In various embodiments, according to such a two-dimensional algorithm,Gain Imbalance values and Phase Imbalance values can be plotted in atwo-dimensional space. Each axis can represent one parameter. Forexample, the horizontal axis can represent Gain Imbalance and thevertical axis can represent Phase Imbalance or vice versa. The range ofGain Imbalance values and Phase imbalance values can be chosen such thatall possibly desirable Gain Imbalance values and Phase Imbalance valuesin the system can be plotted in the two-dimensional space. A series ofgrid-points can be plotted in the two-dimensional space at predeterminedintervals. Each grid-point can represent a Gain Imbalance value and aPhase Imbalance value corresponding to the coordinates of thegrid-point. Accordingly, a Power Estimate can be obtained for eachgrid-point by setting a corresponding Gain Imbalance and Phase Imbalancefor the grid-point in the receiver, conveying a Test Signal in a mirrorfrequency to the receiver, and measuring a Power Estimate of the signalproduced in the receiver for each grid-point. For example, in the systemof FIG. 6, a two-dimensional algorithm can be implemented in digitalcircuits of the IQ Imbalance Estimator 634. According to the algorithm,Gain Imbalance values and Phase Imbalance values can be plotted in atwo-dimensional space. A series of grid-points can be plotted in thetwo-dimensional space at predetermined intervals. A Power Estimate canbe obtained for each grid-point by conveying a Phase Imbalance Estimate640, which can be the phase coordinate of the grid-point, and a GainImbalance Estimate 638, which can be the gain coordinate of thegrid-point, to the IQ Imbalance Compensator 612 and setting acorresponding Gain Imbalance adjustment and Phase Imbalance adjustmentin the receiver. A Test Signal 628 in a mirror frequency can begenerated in an Auxiliary Synthesizer 629, the Test Signal 628 can beconveyed to the receiver, a power of the signal produced in the receivercan be measured in the Digital Power Estimator 632, and the PowerEstimate 636 can be conveyed to the IQ Imbalance Estimator 634. Theprocess can be repeated to find a Power Estimate 636 for eachgrid-point. Similarly, in various embodiments, this can be performed ina system as described in FIG. 5 and FIG. 6.

In various embodiments, a location of minimum Power Estimate andcorresponding minimal IQ imbalance can be estimated based on themeasured Power Estimates at the grid-points in the search space. In anembodiment, such minimum Power Estimate location can be the grid-pointwith the lowest measured Power Estimate. In another embodiment, suchminimum Power Estimate location can be calculated based on the locationsof various grid-points and their measured Power Estimates. Such aminimum Power Estimate location can provide the calibration settings forthe receiver. Alternatively, such a location can be used to determine asubsequent searching region to obtain more refined calibration settings.For example, after determining a location of a minimum Power Estimate ina search space, the minimum Power Estimate location can be used as thecenter of a second searching region, which second searching region cancover a smaller range of Gain Imbalance values and Phase Imbalancevalues than the previous searching region. Further, grid-points in thesecond searching region can be placed at smaller gain intervals andsmaller phase intervals to each other in order to produce more refinedor accurate calibration settings. A second location of minimum PowerEstimate and corresponding minimal IQ imbalance can be estimated in thesecond searching region based on measured Power Estimates at grid-pointsin the second searching region. Similarly, a third searching regioncovering a smaller search space with closer-placed grid-points centeredon the location of the second minimum Power Estimate can be produced andthe location of a third minimum Power Estimate can be found. Searchingthrough subsequent stages can continue until a sufficiently fineestimate of the Gain Imbalance and Phase Imbalance is obtained or untilthe smallest possible search space has been implemented. In variousembodiments, the gain in the base-band section can be increased insubsequent stages of the algorithm to maintain the power of the PowerEstimate values in a certain range as the power of the signal producedin the receiver decreases due to decrease in overall IQ Imbalance ineach subsequent searching stage. The gain can be increased, for example,by a Base-Band Gain Control signal from an IQ Imbalance Estimatorexample as described in the context of FIG. 5 and FIG. 6

FIG. 8 illustrates a two-dimensional space representing Gain Imbalanceand Phase Imbalance in a search algorithm, in accordance with variousembodiments. As illustrated in the example of FIG. 8, Gain Imbalancevalues and Phase Imbalance values can be plotted in a two-dimensionalspace. Each axis can represent one parameter. For example, in FIG. 8,the horizontal axis can represent Gain Imbalance and the vertical axiscan represent Phase Imbalance; in a different embodiment, the axis canbe reversed. The range of Gain Imbalance values and Phase imbalancevalues can be chosen such that all possibly desired Gain Imbalancevalues and Phase Imbalance values in the system can be plotted in thetwo-dimensional space. In the example of FIG. 8, the range of both theGain Imbalance and the Phase Imbalance is 0 to 255 points, where a pointis a unit of Gain adjustment or Phase adjustment. For example, in theparameters of the example illustrated in the figure, this range cancover all possibly desired values of Gain Imbalance adjustment and PhaseImbalance adjustment in the system that corresponds to the illustratedsearch space. A series of grid-points can be plotted in thetwo-dimensional space at predetermined intervals. In the example of FIG.8, the search space is divided into 32 point by 32 point grids toproduce an 8×8 array of grid-points such as the grid point 800. Eachgrid-point can represent a Gain Imbalance value and a Phase Imbalancevalue corresponding to the coordinates of the grid-point. Accordingly, aPower Estimate can be obtained for each grid-point by setting acorresponding Gain Imbalance and Phase Imbalance for the grid-point inthe receiver, conveying a Test Signal in a mirror frequency to thereceiver, and measuring a Power Estimate of the signal produced in thereceiver. For example, this can be performed in a system as described inFIG. 5 and FIG. 6.

In the example of FIG. 8, the Power Estimate can be obtained at eachgrid-point and compared to find the grid-point with the minimum PowerEstimate. For example, in FIG. 8, a minimum Power Estimate grid-point(MIN) 802 at the coordinates (176, 80) can correspond to the lowestmeasured Power Estimate among the plotted grid-points. The coordinatesof the MIN grid-point 802 can be saved and can be the first guess forthe center of a next searching stage. The MIN grid-point 802 has fouradjacent grids (shaded in gray); the centers of the four adjacent gridsare labeled A, B, C, and D (Centers of four adjacent grids for MIN) 804.A prediction of the Power Estimate at the centers of the four grids A,B, C, and D 804 can be obtained by interpolating the Power Estimates atthe four grid-points on the corners of each grid. For example, the PowerEstimates at the four corner grid-points of each of the four adjacentgrids can be averaged to obtain a prediction of the Power Estimate valuefor each center point A, B, C, and D 804. Namely, a prediction of thePower Estimate at the center point A 806 can be obtained by averagingthe Power Estimates at the grid-points located at (144,48), (176,48),(176,80), and (144,80). The predicted Power Estimates at the centerpoints A, B, C, and D 804 can be compared and the coordinates of thecenter point with lowest predicted Power Estimate can be saved as thesecond guess for the center of the next searching stage, we can callthis point MIN4. For example, in the example of FIG. 8, the center pointwith the lowest predicted Power Estimate of the center points A, B, C,and D 804 can be the point A (MIN4) 806. Further, the coordinates of MIN802 and the coordinates of MIN4 806 can be averaged and the resultinglocation 808, in this case at the coordinates (168,72), can be used asthe center of the 2^(nd) Stage Searching Area 810. The second stagesearching area 810 can be an area that is twice the grid size. Hence,for the 32 pt by 32 pt grid of FIG. 8, the 2^(nd) Stage Searching Area810 can be a 64 pt by 64 pt region that is centered on the location(168,72) 808. Accordingly, a similar procedure can be implemented tofind the location of a minimal Power Estimate in the 2^(nd) StageSearching Area 810 to obtain more precise calibration settings.

FIG. 9 illustrates a 2^(nd) Stage Searching Area representing GainImbalance and Phase Imbalance in a search algorithm, in accordance withvarious embodiments. The region in FIG. 9 can depict the 2^(nd) StageSearching Area 810 produced in the example of FIG. 8. Accordingly, theregion in FIG. 9 is a 64 pt by 64 pt space centered on the location(168,72) 808, 908 derived in the example of FIG. 8. A series ofgrid-points can be plotted in the two-dimensional space at predeterminedintervals. In the example of FIG. 9 the search space is divided into 8point by 8 point grids to produce an 8×8 array of grid-points. The PowerEstimate can be obtained at each grid-point and compared to find thegrid-point with the minimum Power Estimate. For example, in FIG. 9, aminimum Power Estimate grid-point (MIN) 902 at the coordinates (92, 164)can correspond to the lowest measured Power Estimate among the plottedgrid-points. The coordinates of the MIN grid-point 902 can be saved andcan be the first guess for the center of a next searching stage. The MINgrid-point 902 has four adjacent grids (shaded in gray); the centers ofthe four adjacent grids are labeled A, B, C, and D (Centers of fouradjacent grids for MIN) 904. A prediction of the Power Estimate at thecenters of the four grids A, B, C, and D 904 can be obtained byinterpolating the Power Estimates at the four grid-points on the cornersof each grid. For example, the Power Estimates at the four cornergrid-points of each of the four adjacent grids can be averaged to obtaina prediction of the Power Estimate value for each center point A, B, C,and D 904. The predicted Power Estimates at the center points A, B, C,and D 904 can be compared and the coordinates of the center point withlowest predicted Power Estimate can be saved as the second guess for thecenter of the next searching stage, we can call this point MIN4. Forexample, in the example of FIG. 9, the center point with the lowestpredicted Power Estimate of the center points A, B, C, and D 904 can bethe point C (MIN4) 906. Further, the coordinates of MIN 902 and thecoordinates of MIN4 906 can be averaged and the resulting location 908,in this case at (166,90), can be used as the center of the 3^(rd) StageSearching Area 910. Accordingly, a similar procedure can be implementedto find the location of a minimal Power Estimate in the 3^(rd) StageSearching Area 910 to obtain more precise calibration settings.

In various embodiments, the process of searching in subsequent searchingareas can continue until sufficiently accurate calibration settings areobtained; until the grid size in a searching area is a certain value,such as one; or until another parameter is met. For example, in anembodiment, if the grid size in a searching area is one, then the MINpoint, or the grid-point in the searching area where the lowest PowerEstimate is measured, can be used as the optimum point and thecorresponding coordinates of the grid-point can indicate the optimalvalue for Gain Imbalance and Phase Imbalance calibration. In anembodiment, if the grid size in a searching region is two, the center ofthe next searching stage can be the MIN grid-point. Also, in anembodiment, calculating the MIN4 point can be eliminated in searchingstages with grid size of one or two and the center of the next searchingstage can be the MIN grid-point.

In various embodiments, the Base-Band gain can be set at the beginningof each stage. In an embodiment, the Base-Band gain can be higher in asearching stage than in a previous searching stage. Namely, becausegrid-points in a given searching stage can correspond to more idealcalibration values than in a previous stage, the overall Power Estimatesat the grid-points in the given stage can be lower than the overallPower Estimates at the grid-points in the previous stage. Increasing theBase-Band gain for subsequent stages of the algorithm can maintain PowerEstimates within more ideal sensitivity levels of the system components,such as power detectors.

In various embodiments, to achieve stability in convergence, the size ofthe searching area in a searching stage can be smaller than the size ofthe searching area in the previous searching stage (except first stage).For example, the size of the searching area in a searching stage can betwice the grid size used in the previous searching stage, as illustratedin the example of FIG. 8. To achieve faster convergence, the size of thesearching area can be reduced to, for example, half of the grid sizeused in the previous searching stage. Further, the number of griddedpoints can be fixed during the different stages, except for the laststages where the algorithm can be limited when minimum grid size isreached.

FIG. 10 illustrates an example process flow of a searching algorithm,such as the algorithm described in FIG. 8 and FIG. 9, in accordance withvarious embodiments. A searching area can be set 1002. In the firstsearching stage of the algorithm, the searching area can be atwo-dimensional space, with Gain Imbalance values on one axis and PhaseImbalance values on the other axis, where the two-dimensional space cancover all possibly desirable values of Gain Imbalance adjustment andPhase Imbalance adjustment in the system. In subsequent searchingstages, the searching area can be a subset of the previous searchingarea, where the center of the searching area in the subsequent searchingstage is determined in the previous searching stage. The searching areacan be gridded with searching grid-points 1004. The searching area canbe gridded by dividing the searching region into grids of apredetermined size, for example, the searching region can be dividedinto a grid to produce an 8 by 8 array of grid-points. A Power Estimatecan be measured at each grid-point 1006 by producing Gain and Phaseadjustments in the receiver corresponding to the coordinates of thegrid-point and measuring the power of the signal produced in thereceiver from a mirror frequency Test Signal conveyed to the receiver.The Power Estimate at each grid-point can be compared to find thegrid-point with the minimum Power Estimate (MIN) 1008. A decision can bemade as to whether the last stage of the algorithm has been reached1010. For example, if the minimum grid size available in the system wasused in the searching stage, the decision 1010 can be made that the laststage has been reached. If the last stage has been reached, then themost recent Gain Imbalance value and Phase Imbalance valuescorresponding to the MIN grid-point can be used to calibrate the system1018. If the last stage has not been reached, then the Power Estimate atthe centers of the four adjacent squares to the MIN grid-point can bepredicted 1012. For example, the Power Estimates at the corners of eachof the four adjacent grids can be averaged to predict the Power Estimateat the center of the adjacent grid. The predicted Power Estimates at thecenters of the four adjacent grids can be compared to find the adjacentgrid with the smallest predicted Power Estimate 1014. The center for thenext stage search can be determined based on the coordinates of the mostrecent MIN grid-point and the coordinates of the center of the adjacentgrid with the smallest predicted Power Estimate 1016. For example, thecenter for the next stage search can be the average of the coordinatesof the most recent MIN grid-point and the coordinates of the center ofthe adjacent grid with the smallest predicted Power Estimate. Asubsequent searching area can be set 1002 centered on the determinedcenter.

The various embodiments of the invention may also involve a number offunctions to be performed by a computer processor, such as amicroprocessor. The microprocessor may be a specialized or dedicatedmicroprocessor that is configured to perform particular tasks accordingto the embodiments by executing machine-readable software code thatdefines the particular tasks described herein. The microprocessor mayalso be configured to operate and communicate with other devices such asdirect memory access modules, memory storage devices, Internet relatedhardware, and other devices that relate to the transmission of data inaccordance with the embodiments of the invention. The software code maybe configured using software formats such as Java, C++, XML (ExtensibleMark-up Language) and other languages that may be used to definefunctions that relate to operations of devices required to carry out thefunctional operations related to the embodiments of the invention. Thecode may be written in different forms and styles, many of which areknown to those skilled in the art. Different code formats, codeconfigurations, styles, and forms of software programs and other meansof configuring code to define the operations of a microprocessor inaccordance with the embodiments of the invention will not depart fromthe spirit and scope of the invention.

Within the different types of devices, such as computers, laptops, cellphones, PDAs, mobile televisions, personal navigation devices, personalmedia players or other devices that can utilize the embodiments of theinvention, there can exist different types of memory components forstoring and retrieving information while performing functions accordingto the embodiments. Cache memory devices can be included in such devicesfor use by a central processing unit as a convenient storage locationfor information that is frequently stored and retrieved. Similarly, apersistent memory can be used with such devices for maintaininginformation that is frequently retrieved by the central processing unit,but that is not often altered within the persistent memory, unlike thecache memory. Main memory can also be included for storing andretrieving larger amounts of information such as data and softwareapplications configured to perform functions according to the variousembodiments when executed by the central processing unit. These memorydevices may be configured as random access memory (RAM), static randomaccess memory (SRAM), dynamic random access memory (DRAM), flash memory,and other memory storage devices that may be accessed by a centralprocessing unit to store and retrieve information. During data storageand retrieval operations, these memory devices are transformed to havedifferent states, such as different electrical charges, differentmagnetic polarity, and the like. Thus, systems and methods configuredaccording to the embodiments of the invention as described herein enablethe physical transformation of these memory devices. Accordingly, theembodiments described herein are directed to novel and useful systemsand methods that, in one or more embodiments, are able to transform thememory device into a different state. The invention is not limited toany particular type of memory device, or any commonly used protocol forstoring and retrieving information to and from these memory devices,respectively.

Further, within the different types of devices, such as computers,laptops, cell phones, PDAs, mobile televisions, personal navigationdevices, personal media players or other devices that utilize theembodiments of the invention, there can exist different types ofinterface components for conveying and displaying information whileperforming functions described herein. Visual displays such as LCDs andaudio devices such as speakers can be included in such devices todisplay information contained in a received signal in audio and/orvisual format while performing functions of the various embodiments.During operation, these components are transformed into different statesto display various graphical images or to vibrate at various frequenciesin order to convey images and sounds to the user. Thus, systems andmethods configured according to the embodiments described herein canenable the physical transformation of these interface components.Further, systems and methods configured according to the embodiments ofthe invention can enable the transformation of a machine-readablemedium, such as a carrier signal, into a different state, such as animage or a sound wave. Accordingly, the novel and useful systems andmethods described herein allow, in one or more embodiments,transformation of the interface components into a different state andtransformation of a received signal into a different state. Theinvention is not limited to any particular type of interface componentor received signal, or any commonly used protocol for applying suchcomponents and signals.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention is not limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense.

Reference in the specification to “an embodiment,” “one embodiment,”“some embodiments,” “various embodiments” or “other embodiments” meansthat a particular feature, structure, or characteristic described inconnection with the embodiments is included in at least someembodiments, but not necessarily all embodiments. References to “anembodiment,” “one embodiment,” or “some embodiments” are not necessarilyall referring to the same embodiments. If the specification states acomponent, feature, structure, or characteristic “may,” “can,” “might,”or “could” be included, that particular component, feature, structure,or characteristic is not required to be included. If the specificationor Claim refers to “a” or “an” element, that does not mean there is onlyone of the element. If the specification or Claims refer to an“additional” element, that does not preclude there being more than oneof the additional element.

1. A system comprising: a low-IF receiver configured to be tunable forselected channels; a synthesizer configured to produce a Test Signal inmirror frequencies for a selected channel and for conveying the TestSignal to the receiver; and an IQ Imbalance Estimator configured forestimating a phase imbalance and a gain imbalance in the receiver basedon a signal produced in the receiver from the Test Signal.